Many apparatuses incorporate control interfaces or capacitive man-machine interfaces, superimposed on or integrated in a display screen.
These interfaces comprise capacitive measuring electrodes distributed over a detection surface, which are sensitive to the presence of a command object, such as a finger or a stylus.
These electrodes are often made in the form of depositions of layers of materials that are both substantially transparent and substantially electrically conductive, such as ITO (indium-tin oxide).
Configurations of control interfaces are known in which the measuring electrodes are distributed in the form of intersecting rows and columns. In this case, the electrodes extend to the edge of the detection surface and can therefore be directly connected to the control electronics.
The electrodes in rows and columns can be made by two distinct superimposed conductive layers, separated by an insulating layer.
The electrodes in rows and columns can also be made in the form of structures (for example of the diamond type) intertwined integrated into the same conductive layer. Conductive bridges are then made at the intersections between the rows and columns, usually with a thin layer of insulation and a deposition of conductive material or micro-wires. In this case, a configuration is obtained with a single conductive layer, which makes it possible to produce a thinner and potentially less expensive structure.
Also known are configurations of control interfaces in which the measuring electrodes are made in the form of individual electrodes distributed in a matrix arrangement in a conductive layer.
This matrix arrangement of the electrodes has advantages in terms of detection capacity. In particular, if it is implemented with sufficiently sensitive detection electronics, it makes it possible to unambiguously detect several control objects simultaneously, in contact and/or remotely.
Known for example is document WO 2011/015794, which describes a method and a control interface device that makes it possible to simultaneously detect a plurality of control objects in contact with and/or remotely from the interface. This interface comprises a matrix of capacitive measuring electrodes protected on their rear face by an active guard. The capacitive detection electronics make it possible to measure the capacitive coupling between the measuring electrodes and nearby objects (in the so-called “self capacitance” mode). In particular owing to the use of the guard, it has sufficient dynamics and sensitivity to allow the detection of objects in contact with the detection surface, and at a distance of up to several centimeters from this detection surface.
The electric matrix can be made in the form of a conductive layer with an ITO deposition. The active guard can also be made in the form of a conductive ITO layer placed below the layer of measuring electrodes (relative to the measuring zone) separated from that layer of electrodes by an insulating dielectric layer.
Typically, in these configurations, the measuring electrodes are individually connected to the control electronics by connecting tracks that are traced between them in the same conductive layer.
A stray coupling problem may then arise between the connecting tracks and the control objects. Indeed, when the control object is in the immediate vicinity of or in contact with the detection surface above a portion of the connecting track, a stray capacitive coupling is created between this connecting track and this object. This stray capacitive coupling can create a false detection, since it can be interpreted by the detection electronics as a coupling between the object and the measuring electrode to which the connecting track is connected.
The stray coupling between a connecting track and an object has a very low value, since, the track being very narrow, its surface across from the control object is very small. However, it may be sufficient to create disruptions in a capacitive interface capable of detecting objects remotely, since it is of the same order of magnitude as the capacitive coupling that is established between a measuring electrode and an object at a distance from the electrode. Thus, a finger in contact with a connecting track can be interpreted as an object present at a distance from the measuring electrode to which the track is connected.
To correct this problem, it is known to have a conductive layer above the layer of electrodes (relative to the detection surface) with a guard mask. This guard mask is arranged so as to extend above the connecting tracks, and comprises openings across from the measuring electrodes. Thus, a control object near or in contact with the detection surface can only generate capacitive coupling with the electrodes and not with the connecting tracks, since they are protected by the guard mask. Known for example are documents JP 2009-86240 and WO 2014/076363, which describe such configurations.
However, this solution has the drawback of requiring an additional layer of conductive material, which is detrimental in terms of thickness and cost.
The present invention aims to propose a capacitive detection device with individual measuring electrodes that make it possible to resolve the drawbacks of the prior art.
The present invention also aims to propose such a capacitive detection device that makes it possible to minimize the stray interactions with the connecting tracks.
The present invention also makes it possible to propose such a capacitive detection device that can be implemented with a minimum of conductive layers.
The present invention also aims to propose such a capacitive detection device that has a minimum thickness.
The present invention also aims to propose such a capacitive detection device able to be superimposed on or integrated in a display screen, and compatible with the production techniques typically used.